The present invention relates generally to controlled laser oscillators and, more particularly, to an apparatus for controlling high-power laser oscillators while exposing the control elements only to low-power.
Oscillator/amplifier combinations are often used to obtain high-power pulses from a laser where control of the mode structure, frequency, polarization, and pulse shape, or a combination of these features is desired. The control elements are located in the oscillator portion of this combination, since low-power, controlled oscillator output pulses can then be amplified by a laser amplifier in what is commonly termed a master oscillator/power amplifier design or MOPA. See, e.g., U.S. Pat. No. 4,596,017 for "Electron Beam Method And Apparatus For Obtaining Uniform Discharges In Electrically Pumped Gas Lasers," which issued to Charles A. Fenstermacher and Keith Boyer on Jun. 17, 1986, FIG. 5 and the description in Column 4, lines 12-24, wherein a gallium arsenide crystal is used for mode-locking and pulse switching a laser oscillator from which a single pulse is selected to drive a series of laser amplifiers which provide the final output. An alternative to this design is the injection-locked oscillator configuration, where the low-power laser pulses are injected into a high-power gain medium. See, e.g. "Stabilization Of The Frequency Of A Pulse-Periodic TEA CO.sub.2 Laser By Injection Of A Signal From A Low-Pressure cw Laser," by V. Yu. Baranov et al., Sov. J. Quantum Electron., 9, 1456 (1979) and "Mode Selection And Frequency Tuning By InJection In Pulsed TEA-CO.sub.2 Lasers," by Pierre H. Flamant and Robert T. Menzies, IEEE J. Quantum Electron., QE-19, 821 (1983 ).
The MOPA design does not saturate the amplifier section completely, since if the amplifier were to be driven such that saturation were approached, the original characteristics of the driving oscillator pulse would be distorted, thereby degrading the control of the output laser pulse. Therefore, the extraction efficiency of laser energy is poor when laser amplifiers are compared with uncontrolled oscillators having the same gain volume. For long pulses or in the situation where very high gain is desired for efficient energy extraction, pulses from injection-locked oscillators will degrade into pulses characteristic or inherent for that oscillator design. Thus, both designs are limited in their ability to control laser pulses while maintaining high extraction efficiencies. Moreover, both designs utilize two gain media.
Accordingly, an object of the present invention is to provide a high-power, controlled laser oscillator having a single gain volume.
Another object of the invention is to provide a high-power, controlled laser oscillator having a single gain volume where the control elements are only exposed to low-power laser radiation,
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.